A transmitter employs beamforming in order to amplify transmitted signals in selected directions, while weakening them in others. To beamform, the transmitter transmits a signal from multiple transmit antennas, but with individually adjusted phase shifts or time delays. This effectively creates a transmit beam in the resulting transmit radiation pattern of the signal—e.g., through controlled constructive and destructive interference of the phase-shifted signals from individual antenna elements.
Beamforming by network equipment aims to improve the performance of signals received by a wireless device from its serving cell. But, especially if each cell has multiple transmit beams on which the wireless device may be served, beamforming complicates analysis of which candidate cell the wireless device should target for a cell change when signal quality of the serving cell degrades.